The invention is in the field of polishing optical connectors, particularly light waveguides housed in tubular ferrules.
Optical fiber connectors are essential to an optical fiber network. Any link loss budget for a network must consider anticipated losses at each junction between optical fibers.
Typically, light transmissions are propagated from one light waveguide through another by an end to end surface mating of two light waveguides. Very often, such end to end matings are facilitated by the use of tubular ferrules, such as ceramic ferrules, housing light waveguides therewithin. Various commercial connectors house these ferrules and bring ferrules into end to end relationship with each other. Misalignment of the ferrules increases signal loss to the system.
An issue which must be addressed in such connections is how to handle the distance between two ferrules in a connection. Damage can occur to the light waveguide interfaces if they are forced together too roughly. Another problem is transmission loss due to a gap between the ferrules. Such gaps cause problems not only due to light impulses escaping through the gap, but also due to the fact that the gap between the end faces being of a different type (such as air) than the medium within the light waveguides, such as glass.
Even if the ferrule end faces are perfectly aligned, the above "gap" problems can persist if end face polishing of the ferrules results in an undercutting of the light waveguide, or optical fiber, with respect to the ferrule end face. Since undercutting causes a small air gap to be maintained between the light waveguides even in the presence of a perfect ferrule fitting, end face polishing methods must consider this problem. Ferrule end faces may be polished either by hand or by polishing machines which have been on the market for several years. In either case, a liquid polishing agent containing particles is typically used on a polishing surface against which the ferrule and light waveguide end face is polished. It is known to use either diamond or silicon dioxide particles in these polishing agents. The use of diamond particles changes the surface index of refraction of the light waveguide end face, resulting in higher reflection values. The use of softer material such as silicon performs better in this respect, but typically the glass light waveguide end face in preference to the ferrule surface, causing the "undercutting" problems referred to above.
A connector can press a flexible polishing surface to form a cup shape which polishes away the edge of a ferrule, but the use of a flexible surface alone does not solve the undercutting problems.
Therefore, a need exists for a polishing process which can be used with modern machinery and allows the use of the softer silicon dioxide particles but which does not result in glass undercutting.